In modern systems such as, but not limited to, communications systems and radar systems, it is not uncommon to encounter so called ‘interfering’ signal or signals coexisting with a signal or signals of interest. For example, such interfering signals or ‘interferers’ often have a frequency that is near to, but outside of, a band edge of a frequency extent occupied by the signal of interest. In other situations, the interferer may be located inside the frequency extent of the signal of interest. Moreover, in many cases, either the so-called ‘close-in’ interfering signal or the so-called ‘in-band’ interfering signal is a narrowband signal (e.g., a frequency tone) that, at times, may exhibit a time-varying frequency characteristic.
The presence of such interfering signals can and generally does corrupt or interfere with processing of the signal of interest by the system. As such, the challenge facing the system receiver/signal processor is to provide some form of filtering that reduces or eliminates the interfering signal while minimally affecting the signal(s) of interest. Typically, such filtering takes the form of one or more of a notch or bandstop filter, a lowpass filter, a highpass filter and a bandpass filter.
Digital systems and mixed systems, systems having both analog and digital portions, often employ digital filters following an analog-to-digital converter (ADC). Such digital filters provide some or all of the filtering for the system.
The ADC ‘digitizes’ or converts an analog input signal, generally including both the signal(s) of interest and the interfering signal(s), into a digital signal. In addition to digitizing both the signal(s) of interest and the interfering signal(s), the ADC may introduce signal distortions and/or spurious signals such as direct current (DC) offsets and/or unwanted spectral components associated with sampling frequency sub-harmonics. Therefore, systems occasionally employ various forms of specialized digital filtering in an attempt to mitigate the effects of such ADC-related signal distortions and/or spurious signals on the signal of interest within the digital system.
Unfortunately, conventional digital filtering approaches often exhibit rather limited capability especially with respect to the ever-higher digital data rates being employed in many modern systems. In particular, many approaches to conventional digital filtering, while theoretically providing attractive characteristics, simply cannot be realized for data rates associated with current and future digitizing or sampling frequencies. In addition, complexity of such filtering approaches may preclude or at least limit their application in certain modern systems.
Accordingly, it would be advantageous to have an approach for digital filtering that was capable of dealing with the filtering needs of such modern systems while simultaneously having a potential for lower complexity in a practical implementation. Such a digital filtering approach would solve a long-standing need in the area of filtering in digital systems.